In the 3rd Generation Partnership Project (3GPP) Release 14, Device-to-Device (D2D) communications have been extended to support Vehicle-to-Everything (V2x) communications, including any combination of direct communications among vehicles, pedestrians and network infrastructures. In 3GPP Technical Specification (TS) 22.185, V14.2.1, several different use cases for V2x have been investigated:                Vehicle-to-Vehicle (V2V), covering Long Term Evolution (LTE)-based communication between vehicles;        Vehicle-to-Pedestrian (V2P): covering LTE-based communication between a vehicle and a device carried by an individual (e.g. handheld terminal carried by a pedestrian, cyclist, driver or passenger); and        Vehicle-to-Infrastructure/Network (V2I/N): covering LTE-based communication between a vehicle and a roadside unit/network (a roadside unit (RSU) is a stationary infrastructure entity supporting V2x applications that can exchange messages with other entities supporting V2x applications).        
Downlink messages, originated from either vehicle User Equipment (UE) in V2V communications or from a network in V2N communications, are generally intended for a group of UEs within a particular geographical area. Unicast cannot provide sufficient capacity when there is a high traffic load, and broadcast/multicast is naturally an option for efficient delivery of such messages. In LTE, Multimedia Broadcast/Multicast Service (MBMS) has been introduced to provide an efficient mode of delivery for broadcast and multicast services. MBMS transmissions can be provided in a Multicast/Broadcast Single-Frequency Network (MBSFN), where the content of an MBMS bearer (which corresponds to a specific service identified by a Temporary Mobile Group Identity (TMGI)) is transmitted from different cells belonging to one single MBMS area, which can be a very large area. MBSFN transmissions occur over a dedicated multicast transport channel (MCH) over which control signaling (on Multicast Control Channel (MCCH)) and data (on Multicast Traffic Channel (MTCH)) can be multiplexed.
Single Cell Point-To-Multipoint (SC-PTM) has been introduced in 3GPP Release13, where multicasting/broadcasting of MBMS data is limited to a single cell area, and multicast/broadcast transmissions (for both control signaling and data) are sent over Physical Downlink Shared Channel (PDSCH) and scheduled by an evolved NodeB (eNB).
V2x communications can be a local broadcast in a limited area. For example, a message from a UE close to the center of a cell may be intended for UEs served by the same cell, while a message from a UE close to a border of a cell may be intended for UEs served by multiple cells. In the former case, it may be beneficial to broadcast the message in one single cell or even a smaller area for reducing redundancy. In the latter case, it may be beneficial to broadcast the message in multiple cells to ensure that all relevant UEs can receive the message.
To efficiently handle the different cases as disclosed above, a geographical-location-based (or geo-based) transmission has been introduced for V2x downlink messages using MBMS in 3GPP TS 36.885, V2.0.0. First, a V2x application server requests and (pre-)establishes one or more MBMS bearers (TMGIs) to appropriate eNBs. Each MBMS bearer is associated with a particular geographical area consisting of one or more cells, and is only transmitted in that area. Here the geo-based routing is performed at the V2x application server. An originating vehicle UE sends a V2x message, including its geographical location and possibly information on its serving cell, to the V2x application server. The V2x application server first determines a target MBMS service area of the V2x message based on the geographical location of the originating vehicle UE and possibly the information on the serving cell, and then selects the MBMS bearer(s) to be used for transmission of the V2x message in the target MBMS service area. The V2x message is then transmitted over the selected MBMS bearer(s) in their associated cell(s). All vehicle UEs that are served by the cell(s) and interested in the V2x message can receive the V2x message.
However, the above solution of geo-based transmission cannot support any target area smaller than a cell.
In order to provide a finer granularity, the entire network area can be divided into a number of local areas, which can be smaller than a cell. In an exemplary solution, the definition of each local area, i.e., its corresponding geographical location, can be known to both the V2x application server and the UEs, but not to eNBs. An eNB only knows the identifiers (IDs) of the local areas contained or partially contained in its coverage. Each MBMS bearer can be associated with a local area. In order to broadcast a message in a particular local area, the V2x application server informs an eNB of a TMGI and an associated local area ID. The eNB broadcasts the message in its entire cell along with the TMGI and the associated local area ID. The UEs in the cell can determine whether to receive the message or not based on the local area ID, the definition of the local area and its current geographical location. Again, in this solution the geo-based routing is performed at the V2x application server.
In New Radio (NR), both the V2x and the MBMS will continue to evolve. For the V2x communications in NR, the required medium rate could be up to 10 Mbps per device, which is much higher than the V2x in LTE. For the MBMS, an MBMS service area may be adjusted dynamically based on e.g. user distribution or service requirements (which relate to e.g. the required communication range). The conventional geo-based transmission may be inefficient when applied in NR.
There is thus a need for an improved solution for geo-based transmission.